The art in the field of wheel alignment devices and instruments extends back for many years encompassing a variety of designs. In recent years, gages which attach directly to the machined face of wheel hubs, principally by means of a permanent magnet have been in popular use. While these gages have been useful, the majority have been of a common design which makes use of long, tubular level vials having adjacent graduations for indicating a reading opposite the position of the vial bubble. Resolution of readings in this type of vial is limited to the operator's ability to judge the position of the adjacent scale mark relative to the center of the bubble which is normally about five-sixteenths of an inch long. In addition, the long vials are not uniformly accurate in curvature even when internally ground. A further disadvantage of these long tubular vials is their large exposure of glass, making them vulnerable to breakage. Examples of this type of gage in which long vials are used are : U.S. Pat. No. 3,071, 863 and No. 3,234,656 (MacMillan), also No. 2,645,860, expired (Bender).
An example of a wheel alignment gage in which a single short vial is used is found in expired U.S. Pat. No. Re. 24,186 (Castiglia).
A single, short vial is incorporated in the present disclosure in which new and novel features are presented.
The wheel toe measuring feature of the present disclosure provides advantages over that of U.S. Pat. No. 3,135,052 (MacMillan) which incorporates toe measurement means dependent on square and accurate construction of the apparatus. In contrast, the present invention provides high accuracy of toe measurement as a result of discovery of a greatly simplified arcuate method of establishing toe measuring base lines.